The productivity of the intensive poultry industry depends on the control of infectious diseases. In Australia the cost of disease to industry is conservatively estimated at $50 million annually. Whilst diseases can be controlled in part by good hygiene and quarantine measures, the industry must still rely on vaccination to protect flocks. In a commercial situation the difficulty and cost in the administration of suitable preventative or curative agents or adjuvants is caused by the sheer number of poultry to be treated. Thus, vaccines must be cheap, effective and easy to deliver.
Conventionally, vaccines constituting live viral particles have been prepared by virus passage and selection of attenuated forms. Alternatively, killed vaccines were prepared from virulent viruses.
One recent attempt to vaccinate commercial bird flocks against a common viral infection is that described in AU-A-34353/93 (VIROGENETICS CORPORATION). This application describes a recombinant poxvirus such as vaccinia virus or fowlpox virus containing heterologous DNA from the Marek's disease virus which is used as a vaccine to induce an immunological response in a host animal. However, the use of poxviruses has the disadvantage that the immune response of poultry is not sustained sufficiently long enough to generate adequate protection. Particularly, the immunoprotection generated may not be sufficient to protect a bird once maternal antibody has ceased to play a role in antibody mediated immunity.
A different approach has been taken by a group at Medisorb Technologies, Inc., in the U.S. as reported in the journal Genetic Engineering News September 1993. This approach used a conventional Salmonella vaccine encapsulated in a biodegradable microsphere based on polylactic-colycolic acid. The approach requires, however that the microsphere be injected into the bird. This approach is not necessarily commercially feasible for large flocks.
It is thus an aim of this invention to provide a delivery vehicle for heterologous sequences of genetic material that is particularly suited to administration on a large scale.
In particular, it is an aim of this invention to provide or enhance means for the generation and/or optimization of antibodies and/or cell-mediated immunity so as to provide protection against infection with common avian diseases, which means is quickly and effectively administered, particularly to large flocks of poultry, that is, to provide or enhance means for the induction of an antibody response and/or cell mediated response in a recipient which affords the recipient protection against infection with common avian diseases. It is an additional aim to provide a process for preparation of a suitable means for the induction of an antibody response and/or cell mediated immune response so as to protect birds against infection with common avian diseases. It is a further aim to provide a protection strategy.